Isolated Weight Lifting

 

When people lift weights, it is almost impossible to isolate the lifting to a specific muscle due to the body's make up and connections in the brain. Phisiologicly, there are limitations to each muscle. When an isolated lift is attempted and one muscle can't do the job and more are called in that might not act directly on the lift but help in some way, it is called recruitment. Recruitment generally involves using more superficcial muscles than inferior ones and will result in a greater torque beacuse of this. Although due to biochemistry and attachment sites suerfical muscles lack the ability for fine movements that inferior muscles have.

 

Additionally to working against the the force gravity on the arm and the weight, the working muscle must also work against the the tension in the antagonist muscles.

While it isn't programmed into our bodies to calculate the exact mass of a weight we use propreiceptors in our body to qualify weight to ourselves. Propreiceptors are in charge of feeling the forces and pressures put on us.

Frank, Netter. H. Atlas of Human Anatomy

In this picture its shown where the forces conflict in tension. In T1 the biceps pull the forearm into flexion. In T2 the triceps pull in extension of the forearm.

 

 

In this diagram for the arm to stay still, the tension in the bicep must equal the torque of Force of gravity on both the forearm and hand and the antagonist muscle tension of the tricep which can never be fully reduced to a null effect due to activating signals from the brain.

 

If the body is trying to conserve work from this movement, shorter arms, less heavy arms, or less tension in the triceps are the only ways.